Method for producing electrically conductive windshield



Jan. 19, 1965 R. A. GAISER Re. 25,

METHOD FOR PRODUCING ELECTRICALLY CONDUCTIVE WINDSHIELD Original Filed Feb. 6, 1956 5 Sheets-Sheet 1 IN V EN TOR.

BY m?! dyad A TTORNE YS R. A. GAISER Jan. 19, 1965 METHOD FOR PRODUCING ELECTRICALLY CONDUCTIVE WINDSHIELD Original Filed Feb. 6, 1956 5 Sheets-Sheet 2 INVENTOR-v We ATTORNEYS Jan. 19, 1965 GAISER Re. 25,711

METHOD FOR PRODUCING ELECTRICALLY CONDUCTIVE WINDSHIELD Original Filed Feb. 6, 1956 5 Sheets-Sheet I5 22 g 46 59 9 J f a9 21 40 f 41 4f A 22 q 22 1 fly, {O INVENTOR.

9 gm aw% A TTORNE YS Jan. 19, 1965 GAISER Re. 25,711

METHOD FOR PRODUCING ELECTRICALLY CONDUCTIVE WINDSHIELD Original Filed Feb. 6. 1956 5 Sheets-Sheet 4 64 62 6s 65 j) 63 I66 68 6 72 1o zzvmvrox. 15 q a dl/t BY 1 14 @4 5 2066: fawn 1 A TTORN E YS Jan. 19, 1965 R. A. GAISER 25,711

METHOD FOR PRODUCING ELECTRICALLY CONDUCTIVE WINDSHIELD Original Filed Feb. 6, 1956 5 Sheets-Sheet 5 IN V EN TOR.

ZIMe/c A TTORN E YS United States Patent p 25,711 METHQD FGR PRQDUGKNG ELECTRICALLY CONDUCTIVE WHlDSl'llElil) Romey A. Gaiser, lv luncie, Ind, assignor to Libbey- Gwens-Ford Glass Company, Toledo, ()hio, a corporation of Ohio Original No. 2,944,926, dated July 12, 1950, Ser. No. 563,679, Feb. 6, 1956. Application for reissue Aug. 31, 1951, tier. No. 135,386

14 (Ilaims. (U. 156-101) This application is a continuation-impart of my copending application Serial No. 395,399, filed December 1, 1953, now abandoned.

The present trend in automobile body design to afiord greater visual areas has found general acceptance in the increasingly popular one-piece Windshields, which in addition to being curved in their central area and spanning the entire front of the car body, have been further rather sharply curved to include end portions or areas extending rearwardly through the corners and into the side areas of the car body. These Windshields have been identified as Wraparound or, by the more expressive term panoramic indshields.

In accordance with automotive safety codes, Windshields are formed of laminated safety 'glass'which is made up of ,two sheets or plates of glass laminated together with an interlayer of non-brittle thermoplasticmaterial, such as polyvinyl butyral resin. Before the actual laminating, however, the glass sheets or plates are bent in pairs on suitable molds as they are conveyed through the controlled zones of a heated furnace. It has heretofore been conventional practice .to pattern-cut these matched pairs of glass sheets before bending, so that the finished laminated unit would properly conform not only to the streamlined contour of the forward area or front of the automotive body but also to the outline of the windshield opening therein. I

It is an aim of this invention to further increase the pleasure and safety of motoring by equipping such windshields with a transparent film or coating capable of conducting electricalenergy and operating to remove accumulations of ice, frost or fog by internal heating of the glass. In order to provide an electrically conducting film on a surface of one or both of the glass sheets or plates, it has been found advantageous to carry out the filming operation in advance of the bendingoperation or when the sheets or plates are perfectly flat.

This filming operation, briefiy stated, involves the a plication of strips of fusible material in spaced areas and preferably along the opposed margins of a glass sheet and in substantially parallel relation; heating the glass sheet to substantially its point of softening and simultaneously fusing the fusible material to form electrodes or bus bars upon the glass, and then spraying the surface of the heated glass sheet containing said electrodes with a suitable material, such as a tin halide, to form upon said sheet a transparent, continuous though extremely thin electrically conducting coating of tin oxide. During installation of the completed Windshield, the electrodes are connected by suitable leads to a source of controlled electrical current to supply the conducting film.

ice

In order to provide a completely satisfactory Windshield that is bent through its central portion to a relatively shallow curve and in its ends is bent sharply upwardly and is also electrically conductive, methods and techniques which depart in a novel manner from those heretofore considered conventional practice are required. Primarily, a curved windshield of one-piece construction such as a panoramic windshield requires sheets or plates of glass of considerable length, and when bending such sheets or plates in pairs, it is essential that they not only nest accurately with one another but also that they assume an accurate predetermined curvature. I have. found that this can best be accomplished if the glass sheets are bent before being pattern-cut to the outline of the finished windshield. Further, the bending of the sheets in block size facilitates the subsequent cutting of the bent sheets to pattern. I

Further, in producing an electrically conductive wind shield of this type, important advantages are attained when the electrodes and the. electrically conducting film are applied to the glass sheets or platesprior to the bends ing thereof and I have discovered that, when it is necessary to have unfilmed areas on the electrically conducting surface'of the glass for any reason, a much better prodnet is produced when the film is applied over the full 1 area, of the surface prior to. bending, and the unwanted portions of the film are deleted after bending.

It is therefore the primary object of this invention to provide an improved one-piece curved windshield which is also electrically conducting and a'novel method for producing the same.

Another important object of the invention is to provide such a method in which the electrically conducting materials are applied to the glass sheets while said sheets are in a list condition, after which they are bent to predetermined curvatures, then part of the film deleted to produce a multiplicity of electrically conducting areas or v to otherwise produce uniform heating (and) after which (then) the sheets are fabricated into finished Windshields .Another object of the invention .is to provide such a method in which the electrodes are arranged in spaced. relation on a surface of a flat glass sheet, such electrodes being located upon said sheet in predetermined relation with respect to the marginal edges of a pattern outline to.

be cut therefrom; the said flat sheet being also filmed with an electrically con ducting material, then bent, out to pattern, having its film processed to provide uniform heating and laminatedwith component parts to provide a curved windshield having electrically conducting areas.

A further object of the invention resides in the provision of a one-piece curved windshield of the above character having selected areas of electrical conductivity separated by neat narrow lines of non-conductivity.

Other objects and advantages of the invention will become more apparent during the course of the following, descriptionv when read in connection with the accompanying drawings.

In the drawings, wherein like numerals are employed. to designate like parts throughout the same:

FIG. 1 is a view of a rectangular flat sheet of glass to which strips of electrode material have been applied. in. accordance with this invention;

FlG. 2 is a transverse sectional view through a furnace for heating the glass sheet with the electrode material thereon prior to filming;

FIG. 3 is a diagrammatic illustration of one form of apparatus which may be employed to film the heated FIG. is a perspective view of the glass sheet after it has been bent;

FIG. 6 is a perspective view of a sheet cut to pattern from the rectangular glass sheet shown in FIG. 5 and having the contour of the finished windshield;

FIG. 7 is a perspective view of a representative form of one-piece bent windshield produced in accordance with the invention and as installed in an automobile;

FIG. 8 is a plan view of the bent windshield showing one arrangement or pattern of the electrically conducting film and electrodes therefor;

FIG. 9 is a fragmentary plan view of a bent windshield showing a second pattern of the electrically conducting film;

FIG. 10 is a fragmentary plan view of a bent windshield showing a third pattern of the electrically conducting film;

FIG. 11 is a fragmentary plan view of a bent windshield which shows a fourth pattern of the electrically conducting film;

FIG. 12 is a vertical sectional view through the windshield showing one form of connection for the electrodes as taken on line 12-12 of FIG. 8;

FIG. 13 is a vertical sectional view of a modified form of windshield andconnection to the electrodes; 7

FIG. 14 is a similar sectional view showing a further modified form of electrical connection;

FIG. 15 is a sectional view taken on line 15-45 of FIG. 14;

FIG. 16 is a plan view of a bent windshield illustrating one way of connecting the electrodes to a source of electrical current;

FIG. 17 is a similar view illustrating a second type of electrical connection;

FIG. 18 is a fragmentary plan view of a bent windshield wherein spaced electrically conductive areas may be electrically connected and controlled at their respective ends;

FIG. 19 is a modified form of the bent windshield shown in FIG. 18;

FIG. 20 is a diagrammatic showing of a method of deleting selected portions of the electrically conducting FIG. 21 is a diagrammatic showing of another method of deleting selected portions of the electrically conducting material; and

FIG. 22 is a diagrammatic showing of still another method in which all or part of the electrically conducting material may be removed in a given area.

Ordinarily, the fabrication of laminated safety glass is conventionally carried out by the matching of two glass sheets or plates according to optical requirements; forming a so-called sandwich by interposing between the glass sheets a layer of non-brittle thermoplastic material, and then subjecting the laminate to heat and pressure within an autoclave to form a composite structure. For auto motive windows and/or Windshields, the glass sheets or plates, after being optically matched, are usually pattern-cut to the outline of the desired opening of the vehicle and, in the case of Windshields, the pairs of sheets have been, more recently, bentto conform to the streamlined contour of the forward end of the car body. With the advent of one-piece Windshields, however, the heretofore conventional modes of bending have been obviated and new and improved forms of bending have been required to produce the desired curvatures.

As hereinbefore set forth, the newly developed onepiece Windshields, formed by a relatively shallow central curved portion and sharply upwardly curving end portions, and popularly known as panoramic Windshields, permit more complete, unobstructed forward vision with added freedom of sight through the corner areas of the car. The bending of glass sheets or plates for this purpose requires not only the shaping of the central area of the sheet but also the bending of the ends thereof upwardly through a critically sharp curve. The neces sary length of sheet, plus the patterned outline to which it has been previously cut, has heretofore created a serious problem of support for the glass during bending, with the result that the marginal edges of the sheets, when bent in pairs, have sufiered some distortion.

in order to meet this problem, it is herein proposed as previously pointed out, that the glass sheets be bent before they are pattern-cut. This is accomplished by placing two substantially rectangular glass sheets or blanks one upon the other and bending them simultaneously upon a suitable mold. In this way, the marginal portions of the blanks that are supported by the bending mold will be outside of the central portions or areas of the sheets which are subsequently pattern-cut from the blanks and which are laminated with one another to form a windshield of the desired outline and curvature. However, when the finished windshield is to be equipped with an electrically conductive film to remove or prevent ice, frost or fog formation, as herein disclosed, it was also found that most advantageous results could be obtained when the sheet to be filmed was provided with the necessary electrodes and then filmed while still fiat.

When the glass sheet is bent, the electrically conducting film is not adversely affected, but when lines or areas of unfilmed surface are present at opposite ends. of the generally rectangular area before the filmed glass sheet is bent, optical distortion results in these unfilmed areas.

It is believed that this distontion is caused by thermal properties of the film and of the unfilmed area, on the applications of heat to the glass during bending. Ac-

cordingly, I have found that it is important to provide a substantially uniform film over the entire area of the surface of the finished windshield prior to bending. Accordingly, important advantages are obtained when the areas to be free of electrically conducting film are produced after bending.

Preferably lines or narrow areas of film are deleted after bending so that the windshield presents a uniform appearance, and when the areas are deleted after bending much neater lines results in the final windshield with corresponding advantages in the appearance thereto.

As hereinafter described, this invention also involves a novel method of arranging the electrodes on the flat glass blank so that after it is bent and the sheet patterncut therefrom, the electrodes will be properly located and of adequate length to accomplish their purpose.

Referring nowmore particularly to the drawings, there is shown in FIG. 1 a rectangular sheet or plate of glass 2%] which will be hereinafter referred to as the glass blank. cleaned, is provided preferably along its longitudinal axis and adjacent the longitudinal edges thereof with predeterminedly arranged parallel strips 21 and 22 of a fusible material, such as a metal frit or the like, to form electrodes or bus bars. For example, a fired-on silver flux that may be used to form the electrodes may consist of 65.6% silver, 7.8% flux, 18% organic liquid binder, and 8.54% thinner. Whatever its composition, the electrode material is deposited on the surface of the glass blank according to the known outline of the pattern to be cut from the sheet and the opposed longitudinal edges of the pattern-cut sheet. Naturally, the contour of the pattern-cut sheet will vary with the required shape and/or bend of the finished windshield. It is therefore preferable to employ a jig or template by means of which the electrode material will be accurately deposited upon the glass blank to form the electrodes 21 and 22.

After allowing the electrode material to air dry, the glass blank 20 is supported by tongs or the like 23 in vertical relation to a carriage 24 which is provided with wheels 25 traversing a monorail 26, as shown in FIG. 2. The carriage 24 is then moved along the monorail 26 to convey the glass into and through a tunnel-type furnace 27, wherein it is brought to the temperature necessary for The glass blank 20, after being thoroughly filming and for also baking the electrode material on the glass. The furnace 27 can be heated in anysuitable manner, such as by means of electric resistance heaters 28, and may be equipped with baffles 29 to provide a more uniform temperature throughout.

During movement of the glass blank 20 through the furnace, it is heated to substantially the softening point of the glass. Since glass varies and has no precise softening point, it is not practicable to give any exact temperature to which the blank is heated before being'-re moved from the furnace for filming, although .it is in the neighborhood of 1250 F. for ordinary plate glass. The application of the electrically conducting coating to the glass is preferably done by spraying the entire surface of the hot glass blank carrying the electrodes 21 and 22 with a solution of a suitable tin compound, such as tin halide,.until a film of tin oxide of the desired thickness and conductivity is formed although it may be formed in some other manner. However, as shown in FIG. 3, this is accomplished by means of spray guns 30 that are positioned at one side of the monorail 26, beyond the furnace 27 to effect a uniform application of the sprayed solution over the surface of the glass. The

spray guns may be mounted on a wheeled carriage 31 traversing rails 32 which permits the spray from the guns With the blank 20 for optical quality. The thus paired glass blanks are then located one upon the other on a bending mold with the filmed blank preferably on the bottom and with its filmed surface disposed upwardly adjacent the lower surface of the upper blank.

As shown in FIG. 4, the matched glass blanks are preferably supported at their ends upon a mold indicated generally at 33 and which includes a central section a and end sections b and c hingedly connected to the central section as at d. When the glass is sufficiently softened by heating, it settles downwardly upon the mold with the end sections b and c thereof acting to bend or fold the end portions or" the glass blanks sharply upwardly in relation to the more shallow curvature imparted to the glass blanks in their central areas as they settle onto the central section a of the mold.

The blanks, after being properly located on the mold, are carried into and through a furnace 34, upon a roller .conveyor 35, the said furnace being provided with suitable heating means 36. From their initially located posi tion in the flat, as indicated by full lines A in FIG. 4, the glass blanks are heated until they sag into contact with the shaping surfaces 37 of the mold sections a, b and c as shown in broken lines B. From the highly heated bending zone of the furnace 34, the bent glass blanks continue on through a zone of gradually decreasing temperature wherein the glass is slowly cooled and annealed.

Upon completion of the above-described operations,

the glass blanks, and more especially the filmed blank 20, will appear as shown in FIG. 5, wherein it comprises a relatively shallow bent central portion or area e and the more sharply bent end portions or areas f and g. The blank is then scored or cut according to a predetermined template pattern to produce a sheet or plate of bent glass 38 as shown in FIG. 6, which conforms to the outline and curvature of the windshield to be produced. The cut is so made that when completed, the electrodes 21 and 22 will be disposed along the opposed longitudinal edges of the pattern-cut sheet 38 throughout the central portion e thereof. In producing one-piece curved Windshields of considerable length, the

closer together than the central portions thereof.

been found very advantageous since the pattern-cut sheets nest or match more accurately when the cut is.

made. Likewise, by supporting the blank along lines outside of the area of the sheet to be pattern-cut therefrom, the tendency toward distortion of the cut sheet will be minimized.

Before completing the assembly of the lamination, the filmed sheet 38 is treated to provide the desired film area through which current will be carried. This area may be determined by factors such as commercial preference or the purpose for which the windshield will be used. For example, in FIG. 7 is shown a completed windshield 39 installed in an automobile, and in this case only the central portion or area e of the windshield is provided with an electrically conducting coating, the coating having been removed from the bent end portions or areas f and g. This is more particularly shown in FIGS. 8 9 and 10. p

In FIG. 8, the central filmed portion or area of the sheet is indicated at 40 and is carried a relatively short distance outwardly into the end portions or areas 41 of the windshield which are substantially wedge-shaped so that their edges are disposed in converging relation to one another. The electrodes 21 and 22 are of a length coincident with that of the filmed area 4%). It will be noted that the opposite' ends of the electrodes extend slightly into the curved end portions of the windshield as indicated at h, which results in these end portions of the electrodes being In order to compensate for this and maintain a uniform density of current throughout the film with elimination of, hot spots therein, the opposite ends of the filmed area 4t terminate in arcuate lines 42 which linearly have a length substantially equal to a straight line extending transversely between the electrodes at the central portion of the sheet as shown diagrammatically at i. The end portions of the windshield outwardly of the filmed area defined by the curved lines 42 in FIG. 8 do not contain any coatingmaterial. This can be accomplished by suitably masking off said end portions before spraying, but, as pointed out 'above, I have found that an improved article is obtained when the film in these areas is removed or erased after bending. 'When the lines 42, denoting the end limits of the filmed area 40, have been established, the completed windshield will be afforded an electrically conducting area spanning the entire front of the car and extending slightly rearwardly through the corners.

On the other hand, the filmed area may be limited strictly to the central portion of the windshield. For this purpose, and as shown in FIG. 9, the electrodes 21 and 22 do not extend into the'wedge-shaped end portions 41 of the windshield but are limited to the substantially rec tangular central portion where the width between the op posed longitudinal electrodes is substantially equal and constant. The current flow between the said electrodes and through the filmed area 40 will likewise be equal to the end'that the end limits thereof can be determined by the straight lines 43.

It may even be found advantageous to carry the effective filmed area farther out into the curved end portions of the windshield as in FIG. 10. Now since the flow path of the'current is materially shortened (in a straight line) between the curved end portions j of the electrodes, the density thereof is undesirably increased in the-corner areas as to create hot spots. To avoid this electrical disturbance, the ends of the filmed area are defined by a more sharply curved line as indicated at 44. This curvature is such that the electrical current density in these areas will be substantially the same as in the more centrally located areas of the sheet where the electrodes are parallel with one another. I

In each of the above instances, the field of the filmed area is determined and the length of the electrodes is initially established by the extent of the areas of fusible 7 material 21 and 22 deposited on the glass blank 20 while it is flat as shown in FIG. 1. Moreover, by accurately locating such areas through the use of a jig or template, the electrodes will follow the actual edge of the bent and cut sheet 33 as shown in FIG. 6.

A suitably established effective conducting area may also be afforded without complete removal'of the filmed coating from the end areas 41 of the bent sheet 38 as shown in FIG. 11. This may be desirable in the event that the characteristics of the coating tend to impart a distinct, though perfectly transparent, irridescent tint to the normal, clear color of the glass. Without changing this naturally inherent tint or establishing a series of definitely different and undesirable color areas in the windshield, it is possible to separate such areas by means of a narrow open area as shown at 45. For this purpose, the electrodes 21 and 22 may be located on the sheet in accordance with any desired film area as shown in FIGS. 8, 9 and 10. However, as shown in FIG. 11, the electrodes 21 and 22 are substantially the same as shown in FIG. 9 so that the effective electrically conducting film area 40 will be confined to the central portion of the windshield, and, while the end portions 41 will retain the filmed coating they will be separated and insulated from the area 40 by the narrow space 45 that is defined by the parallel lines 46 denoting the spaced end limits of the electrically conducting film area 40 and the non-conducting film area 47.

Preferably, the narrow open area 45 is used rather than having unfilmed areas 41 because the neat narrow strip 45 is hardly noticeable whereas the large adjacent areas make a contrast which is more noticeable to the observer. It is also contemplated that the areas 41 may be separated from the filmed area 40. In all events, it is important to film the entire surface of the windshield prior to bending and remove the sufficient electrically conducting material by the area 41 or 45 after the glass sheet has been bent. This provides for more uniform results during bending and a more accurate and neater spacing of the unfilmed areas.

The electrodes 21 and 22 may be provided with leadin connections according to the desired distribution of electrical current and the potential thereof. As shown in FIG. 8, one centrally disposed lead 48 is provided for each electrode 21 and 22. To allow ample room for attaching the lead, as by soldering, when the Windshield is installed, the inner glass sheet 49 of the laminated windshield may be notched as at 50 in FIGS. 8 and 12. The windshield here disclosed comprises the outer and inner glass sheets 38 and 49 bonded together by an interlayer 51 of a thermoplastic material in a manner well known in the art. Likewise, when additional leads are required, they may be similarly attached when located as shown in FIG. 11 and connected in parallel to the current source. The small notched areas, when the windshield is installed, are located within the continuous groove 52 of the rubber channel or weather stripping 53 which conventionally supports and seals the windshield in the framework of the automobile. The notches are therefore both protected from the atmosphere and hidden from sight. When installed within the channel or weather stripping 53, the lead 50 is passed through an dpening 54 in the wall thereof and may be connected to the source of electricity in any suitable manner.

According to the construction shown in FIG. 13, the outboard" sheet 55 of the lamination may be patterncut to a relatively larger outline than the inboard sheet 56. This will provide a margin on which the electrodes 21 and 22 will be exposed and easily available for attachment of the lead-in connections 57. The connections 57 may be attached singly as in FIG. 8 or can be provided in parallel as shown in FIG. l1.'

For other special installations of the windshield, a connection between the electrodes 21 and 22 and an electrical source can be obtained by means of flexible, spring- 8 pressed contactors of the type shown in FIGS. 14 and 15. For this purpose, and before lamination of the glass sheets, the effective areas of electrodes 21 and 22 are extended around and onto the edge surfaces of the outer sheet 55. This may be accomplished by applying a similar material along the edge of the glass either continuously the full exentof the electrodes or at suitable points therealong. An L-shaped electrode 58 will thus be provided on the marginal area of the sheet and across its adjacent edge.

This electrode 58 as will be seen in FIGS. 14 and 15 is engaged by a strip or bar 59 that is located in the groove 52' of the rubber mounting channel 53. The bar 59 is supported by means of a bowed leaf spring 60 resting on the bottom of the groove. The spring may be provided in its central area with an opening through which the lead-in conductor 61 is passed and attached to the bar 59. In completing this type of windshield assembly, the leads 61 are passed through openings 54 in the channel and the associated bars 59 and springs 60 are located within the groove 52. 'The windshield is then fitted into the groove and when installed will locate the electrodes 58 in engagement with the contacting bars 59.

As above described, the lead-in connections to the electrodes for the electrically conducting film are located with respect to the upper and lower edges of the windshield when in its installed position. It is, however, not absolutely necessary that the connections be made in such areas of the windshield. On the other hand, other locations of the lead-in conductors may be preferable,

being dependent upon the most eflicient positioning of the controls to which they are connected or to the framework of the opening in which the windshield is positioned. For instance, in FIGS. 16, 17 and 18, other methods of arranging the lead-in conductors are disclosed which will enable the extension of the lead-in wires through the car framework for connection to one or the opposite ends of the windshield.

Such an arrangement requires that the electrodes be initially formed in a pattern covering substantially the entire margin of the pattern-cut sheet not only along the opposed substantially parallel longitudinal edges of the central portion but also along the edges of at least one of the bent, wedge-shaped end portions. Thus, the character of the electrodes 62 and 63 will be determined by the ultimate manner of electrical connection and definitely established at the time that the areas of fusible material are applied to the flat glass blanks.

As shown in FIG. 16, the electrode 62 extends along one longitudinal edge of the central portion of the glass sheet and then along one converging side of the curved end portion 64 and terminates in the vicinity of the extreme tip 65. Likewise, the electrode 63 is disposed along the opposite longitudinal edge of the glass sheet and along the convergent side of the end portion 64 to terminate in closely spaced relation to the end of electrode 62. This will permit the lead-in conductors to be attached tosaid electrodes at an extreme end of the windshield. In this instance, the central portion of the sheet is filmed while the opposite end portions 64 are not.

On the other hand, as shown in FIG. 17, one electrode 66 may extend along one longitudinal edge of the windshield and into one end area 64, while the other electrode pattern 67 will extend along the opposite longitudinal edge and into the opposite end area of the windshield. This particular arrangement of the electrodes will thus aifordmeans for connecting a lead-in conductor 68 to one of the electrodes at-each end of the windshield.

This arrangement is also applicable to the embodiment The windshield construction illustrated in FIG. 18 de parts from any previously described in that there is provided a means for controlling the supply of electrical current to individual sections of the windshield. This may be found desirable where it is of advantage to more rapidly heat one-half of the windshield, as for example, to remove ice or frost from the left-hand or drivers side more rapidly than from the right-hand side. By means of rheostat controls, the current supplied to either half of the windshield can be thus monitored. For this purpose, individual coated areas 69 and 7% are formed on the windshield by providing two spaced electrodes 71 and 72 along one longitudinal edge of the windshield and two complementary electrodes 73 and 74 along the opposite longitudinal edge. To further provide two individually controlled film areas, in addition to whatever film coating is removed from the end areas, a space 75 is cleared across the medial area of the blank after it has been bent as shown in FIG. 6. The completed windshield will thus present an appearance substantially as shown in FIG. 18 wherein the two equally spaced pairs of electrodes 71, 73 and 72, 74 are terminated short of each other at their inner adjacent ends to supply electrical current to two separated film areas 65 and 70 which arespaced apart by the clear area or strip 75.

In the windshield construction illustrated in FIG. 19 individual coated areas 76 and 77 are formed on the windshield by clearing a space 78 across the immediate area of the glass sheet after it has been bent and patterncut. Spaced electrodes 79 and 30 are used to provide an electric potential across the filmed area 76 at the op posite sides thereof, and electrodes 31 and $2 are provided along the edges of the sheet at the other end to apply an electric potential to the area 77. in order to prevent the ends of the glass sheet from being overheated by having excessive current passing through that part of .the film, a substantially, nonconductive area 83 is provided along the inner margins of electrodes 79 and 8t) and a similar area 84 is provided along the inner margins of electrodes 81 and 82 at the sharply curved ends of the glass sheet.

Accordingly, the windshield construction illustrated in FIGL19 is similar to that illustrated in FIG. 18 in that there is provided a means for controlling the supply of electric current to individual sections of the windshield, but it diilers in that the end areas are prevented from overheating by having the free narrow areas 83 and 84 which-are substantially nonconductive and adjacent the end portions of the electrodes. This arrangement has advantages over the embodiment of FIG. 11 in which the narrow strip is used to isolate the electrically conducting material at the ends of the windshield and the embodiments in which areas of electrically conducting material are removed from the ends of the windshield because in the windshield of FIG. 19 the nonconducting areas near the edges of the windshield do not show since thesmall areas '83 and 84 are covered by the supporting structure of the windshield as are the electrodes.

Any of a number of methods may be used for deleting portions of the electrically conducting film after the bending step. For example, the electrically conducting film may be deleted chemically by treatment with zinc and an acid solution which provides nascent hydrogen which in turn reduces the metal oxide coating to the metal and the acid removes the metal. Such a method is described in US. Patent No. 2,606,566. However, this method has thedisadvantage of requiring that the areas which are to remain intact must be protected from the treating materials by masking means or the like and it is difiicult to produce a neat line with such a method. Accordingly, it is preferred to use one of the methods hereinafter set forth in details.

In FIG. 20 there is shown a lite of glass 85 having a fired-on electrode 86 and an electrically conducting film 87 of a metal oxide and preferably zinc oxide. In

it) order to remove a portion of the electrically conducting film 87 a layer of an organic material 88 such as glycerine is brushed, sprayed or otherwise applied over the film 87. A carbon electrode 89 is sharpened to a point 90 having a width corresponding to the desired width of the narrow area of material to be deleted. In fact, an ordinary graphite pencil may be used having a rod for the electrode 89 and a wooden sheath which encloses the electrode 89. Preferably, a direct current is used, and the carbon electrode is connected to the positive post through lead wire 91, and the bus bar or fired-on silver strip 86 is connected to negative post or the direct current supply through lead wire 92. However, the film may be deleted when the electrical connection is in the reverse of that given or even when an alternating current is applied. After the electric potential has been connected, the carbon electrode is placed in contacted position, as

shown in FIG. 20, and moved over the surface 87 to form a narrow area of deleted electrical conducting film in the desired pattern.

Generally, any organic liquid may be used, but some are superior to others. For example, light oil may be used but it is not so easily removed as glycerine. Other operable materials may have disagreeable odors or create a fire hazard or for other reasons be inferior to glycerin'e,

but it is to be understood that such materials may be used in the practice of this method of removing electrically conducting material.

Preferably, carbon is usedfor the electrode although other materials may be used, but carbon has the advantageof being easily sharpened to the desired width.

The voltage must be suificient to produce an are through the or anic material, but excessive voltages should be avoided due to excessive temperatures produced thereby. Preferably, the voltage used is between 25 and 100 volts.

Another method of deleting a portion of the electrically conducting film may be accomplished by contacting the film at the place in which deletion is desired with an electrolytic solution and establishing a voltage between the film and the electrolyte. In order to delete a line or narrow strip, it is necessary to confine the contact between the electrolyte and the electrically conducting film to a line having a width the same as that desired in the deleted strip or area. Preferably, the electrolyte is so confined by the use of a draftsmans pen having the electrolyte positioned between the nibsthereof. Other methods of confinement may be used, however, such as masking the film with masking tape, wax, or other means.

In order to delete a wider area the material having the electrically conducting film may be dipped directly into the solution of electrolyte and a voltage potential established between the film and electrolyte. This method is particularly useful when an end area is to be deleted, however, centrally located areas may also be deleted by the dipping procedure simply by masking off the areas which are to remain intact. This prevents contact be tween such portions of the film and electrolyte. The preferred method of deleting a narrow area or line is more fully illustrated in the drawing where there is shown in FIG. 21, a lite of glass 93 having a fired-on electrode 94, and an electrically conducting film 95 of a metal oxide and preferably tin oxide.

In order to remove a portion of the electrically conducting film 95 in the form of a line, a draftsmans pen is used having ends or nibs 96 which are adjusted in the conventional manner to regulate the width of liquid that may be held therebetween. A suitable solution of electrolyte 97, as hereinafter more fully defined, is placed between ,the nibs 96 of the draftsmans pen which serves to conduct an electric current to the electrolyte. Lead wire 98 is electrically connected to the draftsmans pen and is connected to the positive terminal offstorage batteries or other direct current source, and lead wire 9'9 is connected to the bus bar or fired-on silver strip 94 and the negative terminal of the direct current source. Accordingly, a potential is applied directly between the electrolyte 97 and the electrically conducting film 95 to provide the desired electrolytic action at the surface of the electrically conducting film.

In FIG. 22, the other embodiment of the method of FIG. 21 illustrated which is especially applicable to the deletion of larger areas although it should be understood that larger areas may be deleted by the modification illustrated in FIG. 21 simply by deleting a series of contacting lines, or that lines may be deleted by using the embodi ment illustrated in FIG. 22 by masking of all the film except a line before the film is dipped in the electrolyte as hereinafter discussed.

In FIG. 22, there is shown a lite of glass 100 having a fired-on silver strip or bus bar 101 and an electrically conducting film 102. Also there is provided a container 103 having electrolyte 104 contained therein, and an electrode 105 in electrical contact with the electrolyte 104. Lead Wire 106 is connected to the positive terminal of the direct current source and the electrode 105, and lead wire 197 is connected to the negative terminal and to the bus bar 101 as shown.

It should be understood, however, that although the above connections are preferred, the electrically conducing material may be removed when the electrical connection is in the reverse of that given or even when alternating current is applied. Good results are obtained by these electrolytic methods when a 24 volt direct current is used.

If desired a graded film may be obtained by using the apparatus disclosed in FIG. 22 and rapidly dipping the sheet into the electrolyte 104 so that the lower portion thereof is in contact with the electrolyte for a longer period of time than the upper portion thereby providing greater deletion of the lower portion. A uniformly graded film may be produced by turning on the electric current, immersing the lite of glass into the electrolyte 104 at a constant velocity and shutting olf the electric current at the desired time during the immersing thereof to avoid further deletion.

A number of different electrolytes may be used and they may be acids, bases or salts. Generally, the electrolyte should be a strong one in order to achieve the best results. Examples of acids which have proven to be satisfactory are hydrochloric acid, sulfuric acid, and phosphoric acid; examples of salts that may be used are ammonium chloride, sodium chloride, and sodium sulfate; and examples of bases that may be used are sodium hydroxide, potassium hydroxide, and ammonium hydroxide.

When solid materials of the above examples are used, 1

good results are obtained with solutions of from 10 to 25 grams per 100 cc. of water. When the above mentioned acids or ammonium hydroxide are used, the commercial solutions are preferably diluted with water in an amount such that the original solution is 30-50% of the final amount.

In order of preference the stronger hydroxides are preferred, then the acids .and then the salts. When the strong hydroxides are used, the deletion is rapid and complete and such an electrolyte is believed to be the best for use under production conditions. Accordingly, hydroxides of the alkali metals are preferred. It is not known exactly why the concentrated alkali hydroxides solutions provide a complete deletion, but it is thought that the tin oxide may be reduced to divalent tin and that the oxide is then converted to a soluble stannite. When a salt is used, the tin oxide is reduced to metallic tin which remains on the glass surface. This tin film has a sufficiently high resistance that it may be allowed to remain in some instances or it may be removed with acid. When acid is used in the electrolyte solution, the tin oxide is reduced to metallic tin and if the contact with the acids is of a suflicient length of time, the acid causes the tin to dissolve.

When the Windshields are made according to the above ash-4 invention, optical distortion is kept at a minimum and a line of demarkation between electrically conducting film and the glass not having electrically conducting film is a neat straight line so that the resulting windshield has a pleasing appearance. It is important to again emphasize that the film should be applied to the glass before bending and that the removal thereof be done after bending. While certain preferred improvements of deleting the electrically conducting firm have been given for the sake of illustration, other methods may be used, the important thing being that the deletion is done after the glass sheet is bent and of course before it is laminated because the electrically conducting area is preferably kept adjacent the plastic layer within the laminate where it is protected from weather and the like and the electrical connections are kept insulated.

It is to be understood that the forms of the invention herewith shown and described are to be taken as illustrative embodiments only of the same, and that various changes in the shape, size and arrangement of parts as well as procedural changes may be resorted to without departing from the spirit of the invention or the scope of the subjoined claims.

I claim:

1. In a method of producing bent glass sheets having selected surface areas only that are electrically conducing and in which the electrical conductivity results from the presence of an electrically conducting film on said surface areas, the steps of applying the film to a surface of said sheet while in the fiat, heating and bending said filmed sheet, and then removing portions of said film from the bent sheet to restrict it to said selected areas.

2. The method of producing electrically conducting bent glass sheets having selected surface areas that are electrically conducting and whose electrical conductivity results from the presene of a transparent electrically conducting film formed by the reaction of a tin compound on a heated surface on said surface areas, which comprises the steps of applying the tin oxide film to a surface of said sheet while in the fiat, heating said filmed sheet to bending temperature, shaping the heated sheet to a predetermined curvature, and then removing the film from portions of the filmed surface lying outside of said selected areas.

3. The method of producing electrically conductive bent glass sheets, comprising applying a pair of spaced 7 electrodes along opposite margins of a fiat sheet of glass,

applying an electrically conductive coating to the surface of the sheet containing the electrodes and in electric contact with said electrodes, heating and bending the sheet to the desired curvature, and the removing'part of the electrically conducting material to provide uniform heating by said electrically conducting coating when a voltage is applied to the electrodes.

4. The method of producing an electrically conductive bent glass windshield, comprising-applying a pair of spaced, substantially parallel strips of fusible electrode material along opposite margins of a fiat sheet of glass, heating the glass sheet to substantially the point of softening of the glass to fuse said electrode material to the glass surface, applying an electrically conductive coating to the surface of the heated glass sheet containing the electrode material and in electrical contact therewith, heating and bending the glass sheet to the desired curvature, then removing part of the electrically conductive coating, and finally laminating said bent sheet with a second similarly bent glass sheet and-an interposed layer of thermoplastic material to form a composite structure.

5. The method of producing an electrically conductive bent glass windshield, comprising applying a pair of spaced, substantially parallel electrodes along opposite margins of a substantially rectangular fiat sheet of glass, applying an electrically conductive coating to the surface of the sheet containing the electrodes and an electricalcontact with said electrodes, heating and bending the sheet to the desired curvature, pattern cutting the bent sheet to conform to the opening of the windshield, then removing predetermined portions only of the electrically conductive coating, and finally laminating said sheet with a second similarly bent glass sheet and an interposed layer of thermoplastic material to form a composite structure.

6. The method of producing an electrically conductive bent glass windshield, comprising applying a pair of spaced electrodes along opposite margins of a fiat sheet of glass having curved end portions, applying an electrically conductive coating to the surface of the sheet containing the electrodes and in electric contact with said electrodes, heating and bending the sheet to the desired curvature, then removing a narrow strip of electrically conducting material near each end of the bent windshield to reduce the electrical contact of the electrically conductive coating on the curved end portions of the glass sheet in an amount suflicient to keep such coating from being heated as much per unit area as is the centrally located coating when a voltage is applied to the electrodes, and laminating said sheet with a second similarly bent glass sheet and an interposed layer of thermoplastic material to form a composite structure.

7. The method of producing an electrically conductive bent glass windshield, comprising applying a pair of spaced electrodes along opposite margins of a flat sheet of glass having curved end portions, applying an electrically conductive coating to the surface of the sheet containing the electrodes and in electric contact with said electrodes, heating and bending the sheet to the desired curvature, then removing the electrically conducting material from the curved end portions of the glass sheet, and laminating said sheet with a second similarly bent glass sheet and an interposed layer of thermoplastic material to form a composite structure.

8. The method of. producing an electrically conductive bent glass Windshield, comprising applying a pair of spaced electrodes along opposite margins of a fiat sheet of glass, applying an electrically conductive coating to the surface of the sheet containing the electrodes and in electric contact with said electrodes, heating and bending the sheet to the desired curvature, then removing the electrically conducting material at each end of the bent windshield in a gradually decreasing amount from the end to the points of maximum curvature, said electrically conducting material being removed in an amount sufficient to keep the remaining coating from being heated as much per unit area as is the centrally located coating when the voltage is applied to the electrodes, and laminating said sheet with a second similarly bent glass sheet and an interposed layer of thermoplastic material to form a composite structure.

9. The method'of producing an electrically conductive bent glass windshield having a central portion and end portions relatively sharply bent with respect to said central portion, comprising applying a pair of spaced electrodes to a glass blank in a pattern conforming With the margins of a desired Windshield shape from which said desired shape can be cut, applying an electrically conductive coating to substantially the entire surface of the blank containing the electrodes, heating and bending the glass blank to the desired curvature, cutting from said blank along the outer edges of the electrodes a sheet having the pattern of the windshield, then removing the coating material from the curved end portions of the pattern-cut sheet outwardly of the ends of said electrodes, and laminating said pattern-cut sheet with a second similarly bent glass sheet and an interposed layer of thermoplastic material to form a composite structure.

10. The method of producing an electrically conductive bent glass windshield having a central portion and end portions relatively sharply bent with respect to said central portion,comprising applying a pair of spaced strips of fusible electrode material to a glass blank in a pattern conforming with the margins of a desired windshield shape from which said desired shape can be cut, heating the glass blank to substantially the point of softening of the glass to fuse said electrode material to the glass surface, applying an electrically conductive coating to substantially the entire surface of the heated glass containing the electrode material, heating and bending the glass blank to the desired curvature, cutting from said blank along the outer edges of the fused electrode material a sheet having the pattern of the windshield, then removing the electrically conductive coating from the curved end portions of the pattern-cut sheet outwardly of the ends of said electrodes, and laminating said sheet with a second similarly bent glass sheet and an interposed layer of thermoplastic material to form a composite structure.

11. In a method of producing bent and filmed glass sheets in which said sheets are heated to bend the same and are provided with film on selected surface areas only, the steps of applying said film to a surface of said sheets before said heating and bending and removing portions of said film after said heating and bending to restrict the same to said selected areas.

12. The method of producing an electrically conductive bent glass windshield, comprising applying a pair of spaced, substantially parallel electrodes along opposite margins of a flat sheet of glass, applying an electrically conductive coating to the surface of the sheet containing the electrodes and in electrical contact with said electrodes, healing the sheet to bend it to the desired curvature, then removing a portion of said coating attaching lead-in wires to said electrodes at points intermediate the ends thereof, and laminating said sheet with a second similarly bent glass sheet and an interposed layer of thermoplastic material to form a composite structure.,

13. The method of producing an electrically conduc tive bent glass windshield, comprising applying a pair of spaced, substantially parallel electrodes along opposite margins of a flat sheet of glass, applying an electrically conductive coating to the surface of the sheet containing the electrodes and in electrical contact with said electrodes, heating the sheet to bend it to the desired curvature, and then removing a strip of said coating to divide the same into spaced independent areas, and laminating said sheet with a second similarly bent glass sheet and an interposed layer of thermoplastic material to form a composite structure.

14. A method of producing an electrically conductive bent glass windshield, comprising applying an electrode along a margin of a flat glass sheet, applying an electrically conductive coating to the surface of the sheet containing the electrode and in electrical contact with said electrode, heating the sheet to bend it to the desired curvature, then removing a portion of said coating, attaching lead-in wires to said electrodes, and laminating said sheet to a second sheet to form a composite structure.

References Cited by the Examiner The following references, cited by the Examiner, are of record in the patented file of this patent or the original patent.

UNITED STATES PATENTS V 6/51 Linder 156-17 2,614,944 10/52 Lytle 156-106 2,725,320 1 1/55 Atkeson et al. l56,-1 Q2 EARL M. BERGERT, Primary Examiner. 

12. THE METHOD OF PRODUCING AN ELECTRICALLY CONDUCTIVE BENT GLASS WINDSHIELD, COMPRISING APPLYING A PAIR OF SPACED, SUBSTANTIALLY PARALLEL ELECTRODES ALONG OPPOSITE MARGINS OF A FLAT SHEET OF GLASS, APPLYING AN ELECTRICALLY CONDUCTIVE COATING TO THE SURFACE OF THE SHEET CONTAINING THE ELECTRODES AND IN ELECTRICAL CONTACT WITH SAID ELECTROSES, HEATING THE SHEET TO BEND IT TO THE DESIRED CURVATURE, THEN REMOVING A PORTION OF SAID COATING ATTACHING LEAD-IN WIRES TO SAID ELECTRODES AT POINTS INTERMEDIATE THE ENDS THEREOF, AND LAMINATING SAID SHEET WITH A SECOND SIMILARLY BENT GLASS SHEET AND AN INTERPOSED LAYER OF THERMOPLASTIC MATERIAL TO FORM A COMPOSITE STRUCTURE. 